Such devices are also known in the art as dissipating brakes, or energy absorbers. Such devices will be hereafter also referred to just using the term “dissipator”.
In mountaineering, or while working at a certain height and the like, it is possible that a fall occurs. Devices for braking/arresting the fall are known, for example by means of wire ropes provided with a connector getting in bulk against a stop. However, such systems cause sudden decelerations and high peaks of stress.
In order to solve such a problem, devices are known in the art that allow the energy absorption, specifically operating by friction or tearing, and serve to absorb and dissipate the energy built up during the fall.
An example of friction absorber, wherein the energy is dissipated into heat, is disclosed in EP1389481 wherein a cable is forced to slide along a given path, or in U.S. Pat. No. 4,100,996 wherein a sling slides in a sort of buckle.
An example of tear absorber is on the contrary described in the document U.S. Pat. No. 3,444,957, wherein the energy of the fall is dissipated by addressing it to open and move away, by tearing them, proper seams which couple the slings.
Generally, tear dissipators have a failure at an established load, based on the type of seams. The threshold level for the opening of the seams applied on this type of dissipators is such to absorb, at each tear, a certain amount of energy, while allowing the falling body losing altitude.
An aspect to be specifically taken into account is the deceleration the body is subjected to during the fall slowing down. Various studies showed that a person eligible tolerance level is at most 6-9 g of deceleration. If this value is exceeded, there is a major risk of causing eye, brain, spinal and bowel damages, due to sudden slowdown and to the associated pressure which is generated on body backbone or soft parts.
On the other hand, in order to limit the whole fall length, partially originating by the elongation extent of the absorber, there is the tendency to implement high strength seams, so as to immediately dissipate a certain amount of energy and therefore limit the length of the fall.
The dissipator elongation is a function of the energy to be dissipated during the fall. In order to brake a heavy body, for example of 120 kg, falling from a certain height, a remarkable amount of energy has to be dissipated. On the contrary, in order to brake a lightweight body, for example a child weighing 40 kg falling from the same height, a remarkably lower energy has to be dissipated.
As the first seams are teared, the fall energy begins to be dissipated and this carries on until the fall residual energy is not able to tear additional seams. It is easy to understand thus how, the fall height being the same, a lightweight body tears a lower number of seams compared to those teared by a heavier body.
By comparing the fall of lightweight and heavy bodies, given a determined dissipator and being the falling speed independent of the body weight, the fall of the lightweight body will be braked in a smaller space, and thus more suddenly, with respect to what would happen for the heaviest body. Such a deceleration can also become much higher than 9 g. This can thus cause remarkable and relevant physical damages to the lightweight person. In the opposite case, but with similar final effect, a particularly heavy person falling with a device calibrated for lightweights, would easily tear all the seams and would suddenly weight with his own residual energy, and his speed, on the dissipator stop, thus in turn being subjected to strong deceleration.
In order to solve such drawbacks, gradual dissipation devices are further known in the art, i.e. having several stages such to decelerate falls of both lightweight and heavy people, by the same device.
Such a device is described for example in U.S. Pat. No. 7,392,881, wherein by a particular implementation of the sling, after a certain tear length, teared branches are doubled. Neither such solutions completely solve the problem of causing large brakes, and thus decelerations, for some loads.
Consider, for example, as absorber provided with three sets of seams respectively calibrated for braking loads of 40 kg, 80 kg and 120 kg. In other words, consider an absorber wherein a load of 40 kg only tears a first stage of seams, a load of 80 kg tears the first two stages of seams, and a load of 120 kg tears the three stages of the dissipator. However, considering a load slightly larger than one of the afore mentioned stages, for example 45 kg, this wholly tears the first stage, and undergoes to a very sudden deceleration, even much higher than 9 g, next to the beginning of the second stage, this being calibrated for a 80 kg load.
From here the need of providing an absorber that highly gradually dissipates forces and is less prone to sudden resistance differences of the different seams.
Furthermore, it has to be taken into account that, in order to support such loads, the seams of such absorbers have to be made with particularly strong yarns and very numerous stitches. The presence of such stitches could weaken the yarn strength; in fact, during the implementation of the stitches, a needle is used carrying out repeated passages that can cause fiber degradation. Furthermore, since strong yarns are crossed by a lot of seams, the slings of such absorbers are highly bulky and stiff, thus difficult to use, in addition they are particularly expensive to be implemented.
In the case of dissipators operating by friction it has furthermore been ascertained that brakings can be significantly affected by the textile fiber aging over time, which fiber becoming stiffened, highly increases its braking potential and thus amplifies the problem of the sudden deceleration. Thus, it is unwanted to obtain the braking function through friction devices and with marked blockages of the textile fiber.
In view of the foregoing, an object of the present invention is to implement a device for braking the fall, which is suitable for slowing down the fall of a wide range of users, having variable weights.
Additional object of the present invention is to implement a device for braking a fall, which is simple and cheap to be implemented, and which is reliable at the same time.